Paleoclimate: Long-distance relationship

Oxygen isotope variations in Chinese cave deposits have been interpreted as proxies for the East Asian summer monsoon. Numerical simulations suggest the deposits may instead record remote climate changes over India and the Indian Ocean.

Water vapour that precipitates over China during the East Asian summer monsoon comes primarily from the Indian Ocean. Model simulations from Pausata et al. suggest that that the isotopic values recorded by Chinese stalagmites (circle, Hulu cave; star, Dongge cave; square, Songjia cave; diamond, Timta cave) reflect processes over the Indian Ocean and subcontinent, rather than the intensity of the summer monsoon precipitation as previously suggested.

In the past decade, oxygen isotope variations preserved in precisely dated calcite deposits in caves, known as speleothems, have provided an increasingly detailed record of past climate variability. Speleothems from locations influenced by the East Asian summer monsoon span the past four glacial–interglacial cycles. Abrupt climate anomalies during the glacial periods are clearly observed in these records, as are lower-frequency, orbital-scale variations. The associated changes in the oxygen isotope ratios are often interpreted as variations in the intensity of the East Asian summer monsoon. Writing in Nature Geoscience, Pausata et al. present results from a general circulation model that challenge this interpretation, suggesting that Chinese speleothem isotope excursions during Heinrich events actually reflect remote changes in the Indian summer monsoon.

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